The present invention relates to an electric blower incorporated, for example, in an electric vaccum cleaner, and in particular, to a noise reducing construction for the electric blower.
Generally, an electric blower of this type includes an impeller directly connected to a rotary shaft of an electric motor for miniaturization and a discharge air flow from the impeller is returned inwardly to cool the electric motor. The devices in which such electric blowers are incorporated are mainly for home use, and it is desirable that noise emitted from these devices minimal.
Therefore, sound absorbing materials have been provided in respective electric blowers so as to reduce noise with the approach being described, for example, in Japanese Utility Model Unexamined Publication No. 61-188000, Japanese Utility Model Unexamined Publication No. 62-16797, and Japanese Patent Unexamined Publication No. 55-107100. The electric blowers described in Japanese Utility Model Unexamined Publication No. 61-188000 and No. 62-16797 respectively have sound absorbing materials which are mounted on a motor frame or an air guide within a return passage for a discharge air flow. The electric blower descried in Japanese Patent Unexamined Publication No. 55-107100 has a sound absorbing material mounted on passage walls of return guide vanes to absorb noises from a discharge air flow passing through the passage.
Further, in the electric blower shown in Japanese Patent Unexamined Publication No. 60-33000, plural openings are formed in portions of a fan casing which face a passage for a discharge air flow in the fan casing, and those openings are covered with a sound absorbing material. When a discharge air flow passes through this passage, parts of the discharge air flows through the openings out of the casing so that the sound absorbing material can absorb noises from the air flowing out of the casing to thereby reduce noise.
Japanese Patent Unexamined Publication No. 62-16798 also discloses an electric blower having a sound absorbing material, wherein a space for absorption of noise is defined between an outer wall of an electric motor and a motor frame and the sound absorbing material is arranged in the space.
U.S. Pat. No. 4,120,616 proposes an electric blower in which a sound absorbing material is installed in an area in which a cooling air for a motor collides so as to reduce generated noise.
An electric blower having a relatively small axial length is also proposed in U.S. Pat. No. 4,757,285.
Considering the use of this type electric blowers as described above, it is desirous for them to have a structure which is compact and low in noise.